The major causes of blindness include cataracts, glaucoma, age-related macular degeneration, diabetic retinopathy, as well as pathological myopia. Of these, vision lost in cataracts can usually be restored by replacing the opacified crystalline lens with an artificial intra-operative lens. However, in many of the other diseases such as glaucoma and AMD, vision loss tends to be permanent and irrecoverable. Hence, there is considerable public and clinical interest to detect such diseases in as early a stage as possible, in order to save sight and reduce the costs of treatment. Early detection is often further complicated by the asymptomatic nature of many eye diseases, in which visual symptoms are usually only observed by the patient at an advanced stage of progression.
The retina is a layer of tissue which lines the inner surface of the eye. It is the light-sensitive part of the eye, on which the lens focuses light, which are then transmitted to the brain as signals for interpretation. Damage and degeneration of the retinal layer are key causes of permanent visual loss. In particular, there are two key areas within the retina known as the optic disk and the macula which have principal roles in the human visual system. These areas are marked on FIG. 1, which is a fundus image of the rear of an eye.